First rule of hiring … record every tiny scratch and blemish before setting off. And get the list signed.
Photograph: Alamy

I recently booked a small automatic car from Green Motion car hire in Leicester. When I arrived the model was not available and I was talked into an upgrade to a Toyota Prius. After 30 hours flying from Australia and a long coach ride, I did not pay full attention when a staff member inspected the vehicle prior to my taking it. The car appeared to be in good condition except for a few minor scratches. I did not expect to have to crawl around inspecting the underside.

I drove the car extremely carefully. I did not mount any kerb when parking or go roughly over speed humps. When I returned, the Green Motion staff member examined the car and found a small blemish on the bumper’s underside. This was only fully visible when kneeling down.

The area had not been scuffed from front to back, as it would have been if going over a kerb. I asked to see the manager who went into what appeared to be a well rehearsed speech. He told me that the price for repair was £500. Eventually he reduced it to £351. He continually said this was the price charged by the Green Motion’s repair contractor. How the contractor knew what to charge without seeing the work that had to be done, I do not know.

The manager then retreated to the office until I left.

I have repeatedly asked, by email, for Green Motion to supply a detailed invoice from the contractor but none has arrived. I have searched the internet and found many other similar accounts – that is, on returning the car a scratch has mysteriously appeared. PJ,Australia

We recently hired a car from the Gatwick branch of Green Motion. Our first impression of the company was not good as we had a 45-minute wait at the airport for its shuttle bus which brought us to an off-airport office, where we had another 30-minute wait before being served.

When we were given the car there were a number of scratches and marks on the bodywork as well as scratches and scuff marks on the front wheels. We pointed these out to the staff member whom we thought was taking notes of all of these marks.

When we returned five days later, a different staff member examined the car and proceeded to inform us that one of the scratch marks on the door was no longer a scratch but had become a dent. We were astonished at this finding as it looked exactly the same as the day we collected it. He then found a scratch on one of the front wheels; we insisted this was also present when we collected the car. It soon emerged that his colleague had not noted these.

After much debate, he agreed that the scratch on the door would remain a scratch, however the scratch on the wheel would remain as a new damage. He proceeded to take €1,403 (£1,030) from my Visa card.

The rental of a Peugeot 308 for five days at a cost of €75 did seem too good to be true – and so it proved. AM,Ireland

Green Motion is a car rental company that offers extremely cheap headline prices, but among many happy customers every year there appears to be a significant number who complain that damage which they did not cause is found when they return the car. This is the allegation from these two renters and more people are complaining of the same online.

Are these customers trying to get away with damage they have caused, as Richard Lowden, Green Motion’s international chairman, claims? Or is there a persistent pattern of this happening to Green Motion customers?

We asked Lowden to investigate the two cases above. After re-examining them, he told us that both charges were fully justified.

He says that both customers signed the paperwork – including the vehicle condition report – before they took the cars. In the first case, the industry body, the BVRLA, reviewed the case and found that the charge was fair and justified and should stand, he said.

In the second case, he accused the reader of exaggerating because the total charge for the damage caused was in fact £186 “in line with Green Motion’s price matrix” including an administration fee of £48.

“All customers are given the opportunity and are requested to inspect the hire vehicle prior to taking it out on hire,” he says. “Once a vehicle is returned, the vehicle is inspected to identify whether or not the customer has caused any damage to the vehicle while it was in their custody.”

The problem which both these renters have is that they didn’t follow the first rule of hiring a car – mark every scratch and blemish on the rental agreement and get it signed before you leave the car park. If you fail to do so, you are immediately opening yourself up to being told by car hire staff that you damaged the car, whether you did or not. It is naive in the extreme to trust the staff to do this for you.

Both writers are adamant that they did not damage the cars.

Meanwhile, we also sent Green Motion a letter we received from a third reader, who had used the firm’s Riga, Latvia, franchise. The company had accused him of causing damage to a car and had, similarly, withheld his £480 deposit at the end of the rental period. Only after spending several days disputing the charge, and after sending many emails and copies of the paperwork (including previously marked damage), did the firm admit a mistake had been made and that he should not have been charged.

When he asked for £160 compensation for the time he spent resolving the matter, the customer was accused of trying to blackmail the company and threatened with lawyers. Lowden says the reader was trying to “leverage the threat of publicising his experience through social media channels and through the press” and that his company would not tolerate being blackmailed.

In the meantime, we would advise potential renters thinking of using this firm, or any other car hire company, to scan the internet for reviews before they hand over their card details. And always take videos/photographs of the car when hiring and ensure that any marks, damage or blemishes are identified, agreed with the hiring firm and signed for.

Trustpilot lists Green Motion as its worst car hire company, ranking it 77 out of 77. Lowden, however, blames these poor reviews on customers airing “their frustrations that they have been caught and required to pay for damage to hire vehicles”.

Unlike other hire firms, he says, he does not put up fake reviews.

We welcome letters but cannot answer individually. Email us at consumer.champions@theguardian.com or write to Consumer Champions, Money, The Guardian, 90 York Way, London N1 9GU. Please include a daytime phone number